RheoDLS@RRI
Highlights of our present research
We use several experimental techniques to understand the strucuture, dynamics, rheology and stability of out-of-equilibrium soft materials. For a recent article I wrote on soft materials and the curious things they do, please look at my recent review article here. For Sanjay's recent RRI newsletter article on the glass transition phenomenon in suspensions of the thermoreversible polymer PNIPAM, please click here. One of our major motivations is to use soft systems as models to understand the physics of out-of-equilibrium hard condensed matter systems. Another is to put these extremely versatile materials to use in a variety of situations related to therapeutics, industry and day-to-day life. We use techniques such as static and dynamic light scattering, oscillatory and rotational rheology, ultrasound attentuation spectroscopy and electroacoustics, high-speed imaging and, more recently, optical tweezers for our studies. Ours is a very interdisciplinary field and we collaborate with engineers, physics and chemists, both theorists and experimentalists, here and abroad. Here are some of the problems that we have been working on recently.
Structure-dynamics correlation in colloidal suspensions
We look at the aggregation of charged colloidal clays in aqueous suspension. In dry form, clay colloids are stacked up as tactoids which exfoliate in suspension. By looking at the attenuation of ultrasound waves by colloidal clay suspensions, we have carefully monitored the swelling and exfoliation of clay tactoids in water. We have also used electroacoustics to estimate the dispersibility and stability of clay suspensions with different levels of charge screening. We uncover very interesting structure-dynamics correlations from our studies.
Relevant Publications
Samim Ali and Ranjini Bandyopadhyay,
Langmuir, 29 , 12663, (2013).
2) Evaluation of the dispersibility and stability of natural clay in aqueous dispersions,
Samim Ali and Ranjini Bandyopadhyay
Applied Clay Science, 203, 85 (2015).
3) Effects of electrolyte concentration on the microstructure and yielding of aqueous dispersions of colloidal clay,
Samim Ali and Ranjini Bandyopadhyay
Communicated (2015).
Ranjini Bandyopadhyay and Samim Ali,
Faraday Discussions (2015).
Aging and rheology of soft glassy suspensions
Clay colloidal suspensions 'age', i.e. their structure and dynamics evolve spontaneously with time because of an evolution of the inter-particle electrostatic interactions, plus due to the swelling/ exfoliation kinetics described earlier. We have performed extensive experiments that show the potential of aging colloidal clay (Laponite RD platelets) suspensions as model glassformers. In a recent work, we have shown that a simple one-to-one mapping exists between the time since preparation of a Laponite suspension and the inverse of the temperature of a supercooled liquids. In another work, we have screened the charges on the Laponite platelets and have performed a DLVO analysis to show the strong possibility of attractive interactions in these otherwise repulsive colloidal suspensions. Check below for our publications in this area.
Relevant Publications
1) Investigation of the dynamical slowing down process in soft glassy colloidal suspensions: comparisons with supercooled liquids,
Debasish Saha, Yogesh M. Joshi and Ranjini Bandyopadhyay,
Soft Matter, 10 , 3292 (2014).
2) Dynamic Light Scattering Study and DLVO Analysis of Physicochemical Interactions in Colloidal Suspensions of Charged
Debasish Saha, Ranjini Bandyopadhyay and Yogesh Joshi,
Langmuir, 31, 3012 (2015).
3) Kinetics of the glass transition of fragile soft colloidal suspensions,
Debasish Saha, Yogesh Joshi and Ranjini Bandyopadhyay
Communicated (2015).
arxiv.org/abs/1506.02971
4) Characteristics of the secondary relaxation process in soft colloidal suspensions,
Debasish Saha, Yogesh Joshi and Ranjini Bandyopadhyay
Communicated (2015)
arxiv.org/abs/1508.05758
5) Debasish Saha, PhD thesis (2015)
6) Stress relaxation in aging soft colloidal glasses,
Ranjini Bandyopadhyay, P. Harsha Mohan and Yogesh M. Joshi,
Soft Matter, 6, 1462, (2010).
Novel complex fluids systems: micellar copolymer solutions, biopolymer gels and concentrated colloidal suspensions
We have also looked extensively at self-assembled systems. We have addessed how anisotropic and polydisperse copolymer micelles pack in an aqueous solution. We have even shown recently that Pluronic copolymer micelles in aqueous media can be fantastic capsules for targeted and controlled drug delivery. We have looked at the formation and rupture of biopolymer pectin gels that are the main ingredients of plant cell walls and therefore decide their rigidities. We have also seen some evidence of rheological chaos in concentration suspensions of cornstarch, a colloidal system comprising anisotropic disks.
Relevant Publications
1) Phase behaviour and dynamics of a micelle-forming triblock copolymer system,
Paroor Harsha Mohan and Ranjini Bandyopadhyay,
Phys. Rev. E 77, 041803, (2008).
Rajib Basak and Ranjini Bandyopadhyay,
Langmuir, 29 (13), 4350, (2013).
Rajib Basak and Ranjini Bandyopadhyay,
Langmuir, 29 (13), 4350, (2013).
4) Formation and rupture of Ca2+ induced biopolymer pectin gels,
Rajib Basak and Ranjini Bandyopadhyay,
Soft Matter 10 (37), 7225, (2014).
4) Rajib Basak, PhD thesis (2015)